Electronic devices such as field-effect transistors (FET's) are conventionally formed on a substrate, such as a silicon semiconductor substrate or an insulating substrate, and are combined with interconnections to form integrated circuits, which may be used, for example, as an array of transistors to address pixel elements in displays. The integrated assemblies have typically been built up by forming a number of layers, each layer being formed by depositing a film of semiconductor, insulator or electrical conductor material and by subsequently patterning the film of deposited material, typically by photolithography in a subtractive process (i.e., a portion of a blanket-deposited film is selectively removed). Conventionally, fabrication of semiconductor devices uses a number of different processes performed sequentially, and such sequential methods can increase the time, and therefore the cost, of device fabrication.
Inorganic semiconductive films have been formed by many known methods, including deposition by evaporation, chemical vapor deposition, physical vapor deposition (i.e., sputtering), etc., and subsequent patterning by photolithography.
Inkjet printing methods have been used for many purposes, including ordinary printing of ink on paper, formation of 3-dimensional objects, deposition of photopolymerizable solutions for photolithographic patterning, printing of color filters for liquid-crystal displays, printing of light-emitting layers for electroluminescent devices, printing of conductive traces on circuit boards and integrated circuits, and many other purposes.
Organic semiconductor films have been inkjet printed, and these materials are suitable for some applications, but they have not provided carrier mobilities (i.e., for current drive capability) achievable with inorganic semiconductor films. Another well-known disadvantage of organic semiconductors is that the performance (e.g., on-to-off current ratio) strongly declines over a relatively short period of time, which precludes their use for long-term-use products (e.g., two years or more of use).
Inorganic thin-film semiconductors of polycrystalline silicon and amorphous silicon have many attractive qualities, including lifetime and performance qualities, but patterned films of polycrystalline silicon or amorphous silicon have not been prepared successfully by any additive process.
Thus, there is a need for efficient and economical methods for forming patterned inorganic semiconductive films.